Process for the production and purification of benzoic acid

ABSTRACT

PRODUCTS CONTAINING AT LEAST 99.8% OF BENZOIC AND LITTLE OR NO HIGH BOILING IMPURITIES ARE OBTAINED BY A PROCESS IN WHICH TOLUENE IS OXIDIZED UNTIL ABOUT 25% TO 45% OF IT IS CONVERTED TO BENZOIC ACID, THE BENZOIC ACID IS CRYSTALLIZED FROM THE REACTION MIXTURE, AND AFTER WASHING WITH TOLUENE THE CRYSTALLINE BENZOIC ACID IS DISTILLED. FROM 10% TO 100% OF THE COMBINED MOTHER LIQUOR AND TOLUENE WASHES IS PURIFIED BY DISTILLATION BEFORE BEING RECYCLED.

June 11, 1914 H sin. E111 PROCESS FOR THE PRODUCTION AND PURIFICATION OF BEHZOIC ACID Filed Oct. ll. 1968 United States Patent Oliice 3,816,523 Patented June 11, 1974 3,816,523 PROCESS FOR THE PRODUCTION AND PURIFICA- TION OF BENZOIC ACID Henri Sidi, Paramus, and Michael Sidey, Garfield, NJ., assi ors to Teuneco Chemicals, Inc. Filed Oct. 11, 1968, Ser. No. 766,835 Int. Cl. C07c 63/02 U.S. Cl. 260-524 R 9 Claims ABSTRACT OF THE DISCLOSURE Products containing at least 99.8% of benzoc and little or no high boiling impurities are obtained by a process in which toluene is oxidized until about 25%. to 45% of it is converted to benzoic acid, the benzoc acid is crystallized from the reaction mixture, and after washing with toluene the crystalline benzoc acid is distilled. From 10% to 100% of the combined mother liquor and toluene washes is purified by distillation before being recycled.

This invention relates to a process for the production and purification of benzoc acid. More particularly, it relates to an integrated process for the conversion of toluene to benzoc acid by catalytic liquid phase air oxidation, crystallization of benzoc acid from the oxidation mixture, and distillation of the crystallized benzoc acid which yields products of very high purity.

Benzoic acid produced by the oxidation of toluene with an oxygen-containing gas in the presence of a heavy metal oxidation catalyst is normally contaminated with impurities which may be derived from impurities in the feedstock or formed as products of secondary reactions. Such impurities include benzaldehyde, benzyl alcohol, esters of benzoic acid, diphenyls, p-phenylbenzoic acid, phthalic anhydride, and related compounds Which have vapor pressures and solubilities close to those of benzoc acid and are consequently diiiicult to remove from the product by any of the previously known procedures. Contaminants of this type are highly undesirable because they cause the product to be unsatisfactory with respect to color and odor and because they may interfere in chemical conversions in which the benzoc acid is used as a reactant.

In accordance with this invention, it has been found that a product that contains at least 99.8 percent of benzoic acid and little or no contaminants that boil at approximately the same temperature as benzoc acid or at higher temperatures can be prepared in a nearly quantitative yield by an integrated process in which toluene is converted to benzoc acid by catalytic liquid phase air oxidation, benzoc acid is crystallized from the oxidation mixture, and the crystalline benzoc acid is distilled. From 10 percent to 100 percent of the combined mother liquidtoluene washes is distilled to separate its volatile components from the catalyst and high boiling impurities before the mother liquor is recycled to the reactor.

For a more complete understanding of the invention, reference should be made to the accompanying drawing, which is a block diagram illustrating the various essential sequential steps and other features of this process for the preparation and purification of benzoc acid.

The process of this invention is generally carried out as an integrated series of runs in which the starting material for each run after the rst is the combined mother liquortoluene washes from the preceding run, a portion or all of which has been distilled to separate the unreacted toluene and other volatile compounds from the catalyst and high boiling impurities. In this way, a series of sixteen or more runs can be carried out in Which the yield and quality of the benzoc acid obtained from the linal run are not substantially different from those obtained from the initial runs.

In the oxidation step of the process, toluene or the puried mother liquor from a preceding run is introduced into a reactor. A11 oxygen-containing gas, which is preferably air, is introduced into the bottom of the reactor and is allowed to bubble through the toluene feedstock. The conversion of toluene to benzoc acid is effected in the presence of a heavy metal oxidation catalyst, such as cobalt acetate, cobalt octoate, cobalt benzoate, cobalt naphthenate, manganese acetate, manganese octoate, and the like. 'Ihe amount of catalyst used is generally in the range of about 0.01 percent to 5 percent or more and preferably about 0.1 percent to 1 percent of the weight of toluene present in the reactor. The oxidation reaction is effected at a temperature in the range of about 130 C. to 200 C., preferably 150 C. to 175 C., at a pressure sufficient to maintain liquid phase reaction conditions, that is about 2O p.s.i. to 100 p.s.i., and preferably 50 p.s.i. to 75 p.s.i.

If a product having the desired quality is to be obtained, the reaction should be terminated when about 25 percent to 45 percent and preferably about 35 percent of the toluene has been converted to benzoc acid During the oxidation, a vapor stream containing inert gases, toluene, and water is removed from the reactor, cooled to condense toluene, passed through a Water separator and a column packed with carbon, and then discarded.

The reaction mixture is cooled to -90 C. and removed from the reactor. After the addition of the toluene that collected in the carbon column, the reaction mixture is heated to redissolve any precipitated solids and then cooled to a temperature below 50 C. and preferably to room temperature with stirring to precipitate crystalline benzoc acid. The benzoc acid is separated from the mother liquor by centrifugation, filtration, or other solid liquid separating technique. The benzoc acid cake is washed with fresh toluene and dried.

'I'he crystalline benzoic acid is further purified by distilling it at a pressure in the range of about 50 mm. to 760 mm., and preferably about mm. Highest yields of distilled benzoc acid are obtained when each batch of crystalline benzoic acid is added to the residue from a previous distillation -before being distilled.

As has been indicated, the mother liquor obtained when the crystalline benzoc acid was separated is combined with the toluene -washes and subjected to some purification before it is returned to the reactor and subjected to oxidation. The purification can be carried out by any suitable and convenient procedure that removes from it at least a portion of the high boiling impurities and catalyst. One procedure that gives excellent results involves separating the combined liquor into two portions, each of which comprises about 10 percent to 90 percent of the liquor. The first portion is returned without purification to the reactor. The second portion is distilled iirst at atmospheric pressure and then at about 50 mm. to 200 mm. to a temperature of about 200 C. to 225 C. to separate a fraction containing unreacted toluene, benzoc acid, and volatile impurities from the residue that contains the catalyst and higher boiling impurities. The volatile fraction and an amount of fresh catalyst equivalent to that in the distillation residue are then charged into the reactor. Particularly satisfactory results are obtained when about half of the mother liquor is returned to the reactor without purification and the other half is purified by distilling it first under atmospheric pressure and then at a pressure of about 100 mm. to 210 C. When the mother liquor is treated in this Way, a series of sixteen or more runs can be made without significant change in the yield and quality of benzoc acid obtained or in the amount of non-volatile impurities in the mother liquor.

TABLE IV [Series of runs lor the preparation of crystalline benzoic acid in which 50% Analysis of product by vapor phase chromatography, percent Di- Benzyl acid Toluene phenyls benzoate of the benzoic acid mother liquor was purled prior to recycling] Amount oi benzoic acid isolated Benzolo (grams) n 111 1113 23 MOONMMWM OOOOMOOMH 0000.0.0.0.0. 0.0.0.0.0.0.0.0.0.

3 597648760 638 50 maaaammammaamaaa ing mix- Run number due of the distillation of Example 1. 'Ihe result ture was distilled by the procedure described in Example 1.. The main cut, which Was obtained in a recovery of 100%, had the following characteristics Analysis (byvapor phase chromatography) (percent) lAter Run 9, 90% of the combined mother liquor-toluene Wash was uiifed by distillation prior to its use in Run 10.

i Runs 1'( and 18 exhibited unsatisfactory wringing and washing characteristics, probably because of the accumulation of impurities, eg., p-phenylbenzoic acid, for which the product Was not analyzed.

Benzyl diphenyl benzoate Unknowns TABLE III [Reaction by-productsbed on toluene-tree benzoic acid mother liquors after each of the runs] Analysis of toluene-tree benzoic acid mother liquor percent Benzyl Phthalic 2-methy1- B-meth alcohol anhydride diphenyl Benzaldehyde 040.2392203426647 LLLQLQLQLLLLLLZS 5690111195444578 0.0.0.LLLLL0.0.0.0.00.00

515.1267869677893 QLL2.2.2.92.ZL1L1112 aO.0.0.0.0.L0.0.,0.0.0.0.0.0.0.

Samples of the mother liquors obtained from each of f the runs in this series were analyzed. The amounts of reaction by-products in these samples are set forth in 50%v of which had been purified by distillation, were 45 Table V.

. TABLE V [Reaction by-products based on toluene-free benzoic acid mother liquors] Analysis of toluene-free benzoic acid mother liquor, percent Benzal- Benzyl Phthalic 2-methy1- 3-meth Benzyl dehyde alcohol anhydride dlphenyl dipbenyl benzoate Unknowns a series o EXAMPLE 3 Using the procedures described in Example 1 runs was carried out in which recovered mother liquors,

Mother liquor obtained from rim 015463092435150014 IILLLLZLZL1121LLLL 4554444.33454654566 0D.0.0.0.n0.0nw0.0.0.0.00.0.0.0.

58999004980224511144 0.0.0.0.0.LLO0.LLLLLLLLL 00.0.0.00.nu.n0.0.00.LL0.0L0.

50000432647687555344 0.0.0.0.O.0.L0.20.n0.0.0.000nw EXAMPLE 4 Using the procedures described in Example 1, but using manganese octoate instead of cobalt octoate as the catalyst, a series of runs was carried out in which recovered 70 mother liquors, 50% of which has been puritied by distillation, were oxidized at 150-155 C. using air at the rate of 2.5 cubic feet per hour at pressure of 55 d at least 99.9 perpounds per square inch until 35 percent of the toluene lly no high boiling was converted to benzoic aci The amounts of crystal- 75 line benzoic acid recovered in seven consecutive runs oxidized at 15CI-155"` C. using -airat-the rate of 2.5 cubic feet per hour at a pressure of 55 pounds per square inch until 29 percent of the toluene was converted to benzoic acid. The amounts of crystalline benzoic acid recovered in eighteen .consecutive runs and the analysis of the products are set forth in- T able'IV.

Distillation of theproducts of these runs by the procedure described i'n ExamplesV land -2 gave nearlyquantitative yields of products that containe cent of vbenzoic acid vand substantia and the analysis of the products are set forth in Table VI.

Distillation of the products of these runs by the procedure described in Examples land 2 gave nearly quantitative yields of products that contained more than 99.9 percent of benzoic acid and substantially no high boiling impurities.

TABLE VI [Series of runs for the preparation of crystalline benzoic acid using manganese octoate as catalyst and purifying 50% oi the mother liquor prior to recycling] lAmount; Analysis of product by vapor phase of benzoii. chromatography, percent isolated Benzoic ADlphen- Benzyl Run number (grams) acid Toluene yls benzoate n 347 99. 85 0. 11 0.02 0.02 2 (recycle) 361 99. 86 0. 04 0. 005 0. 05 3 recycl 380 99. 86 0. 06 0. 005 0. 06 4 recyc 376 99. 52 0. 09 0. 00 0. 03 5 reeyc 360 99. 69 0. 11 0. 01 0. 06 (i'ecyc 324 99.64 0.21 0. 01 0.08 7 (recycle) 262 98. 85 0. 24 0. 11 0. 64

Norm-The oxidation in Run 7 took place very slowly (l2 hours versus the usual 5.5 hours when a manganese catalyst is used), probably because of the accumulation ci impurities, o g., p-phenylbenzoie acid, for which the product was not analyzed.

COMPARATIVE EXAMPLE TABLE VII [Series oi runs for the preparation oi crystalline benzoic acid in which the mother liquors were not purified prior to recycling] Amount Analysis of product by vapor phase oi benzoiis chromatography, percent elated Benzoio Diphen- Benzyl (grams) acid Toluene yls benzoate From the data in Table VII, it will be seen that the benzoic acid contents of the products fell below 99 percent after lthe third run. In addition, the isolation and washing of the products became diiiicult at this point.

-Distillation of the products vof Runs 2 and 3 of this series by the procedure described in lExamples 1 and 2 yielded products that contained more than 99.8 percent of benzoic acid and very smallamounts of high boiling impurities. The products obtained by the distillation of the :products of Runs, 4 throngh..7.contained less than 99.5 percent of Vbenzoic acid with most of the impurities present being lphthalic anhydride, benzyl `benzoate, methyldiphenyls, and other'high boiling compounds.

The terms and expressions that yhave been employed are used as terms of descriptionand not of limitation. There is no intention in the .use of. such terms and expressions of excludingany equivalents of vthe features shown and described or portions thereof. lIt is recognized that various 8 modifications are possible within-the scopev of the 4invention claimed. f

What is claimed is: h v y 1. An integrated process for the production and purification of benzoic acid that 4,comprisesY the' following s equential steps: Yl-

(a) contacting in a reactor a feedstock comprising toluene and a heavy metal oxidation catalyst with an oxygen-containing gas in therliquid phase at temperature in the range-of about 130C; tor-200 C. and a pressure in VtheV range ofrrabout 20 p.s.i. to 100 p.s.i., until 25 percent to 45 percent: ofi the toluene has been converted to benzoic acid; 1'

(b) cooling the reaction mixture toga temperature be- 10W about 50 C.; 'i' ,'l .11515 I (c) separating the crystallized benzoic lacidY from the mother liquor; 11"" "f-f (d) Washing the crystalline benzoic acid with toluene and dryingit; l

(e) distilling the crystalline'benzoic acidl ata pressure in the range of about -50- mm. to -760 mm. and recovering a toluene fraction and a benzoic acid fraction;

(f) combining the mother liquor from step (c) lwith the toluene wash from step (d) and therecovered toluene fraction from step (e) to form a combined liquor;

(g) separating the combined liquor into a first portion containing from 10 percent to 100 percent ofthe combined liquor and a second portioncontaining from 0 to 90 percent of the combined liquor;

(h) distilling the -iirst portion of the combined liquor under a pressure of about-50 mm. to 200 mmfto about 200 C. to 225 C.;

(i) charging the distillate from step (h) and the second portion of Vthe combined liquor (step (g))V to the reactor; and v (j) repeating steps (a) through (i). 'i

2. The process of claim 1 wherein the oxidation of toluene (step (a)) is eiectedat atemperature inthe range of 150 C. to 175 C. anda pressure in the range of 50 p.s.i. to 75 p.s.i. i L

3. The process of claim 1 wherein the ,oxidationY of toluene (step (a)) is continued until about 35 Apercen of the toluene has been converted to benzoic acid. l" w' 4. The process of claim 1 wherein in step (a) th oxygen-containing gas is oxygen and the catalyst is cobalt octoate.

5. The process of claim 1 wherein in step (b) the reaction mixture is cooled to room temperature.

6. The process of claim 1 wherein in step (e) the crystalline benzoic acid is distilled under a pressure of about 100 mm.

7. The process of claim 1 wherein the reaction mixture obtained from step (a) is cooled to a temperature in the range of 80-90 C., removed from the reactor, heated to dissolve precipitated solids, and then cooled to a temperature below about 50 C.

8. 'Ihe process of claim 1 wherein in step (g) each of uv the portions contains about 50 percent of the combined liquor.

9. The process of claim 1 wherein in step (h) the distillation is carried out under a pressure of about mm.

References Cited v UNrrED sTArEs PATENTS.,

P. I. KILLOS, Assistant Examiner f *y 5^ l U.s.`c1 xn. 

